1. Field of the Invention
The present invention relates to a zoom lens and an optical apparatus having the zoom lens, and more particularly to a zoom lens suited for a film still camera, a video camera, a digital still camera or the like, which has three lens units in which a lens unit of negative refractive power leads, and which has the entirety of a lens system thereof reduced in size by appropriately setting the lens construction of the respective lens units.
2. Description of Related Art
In recent years, with the advancement of high performance of an image pickup apparatus (camera), such as a video camera or a digital still camera, using a solid-state image sensor, a zoom lens having a large aperture ratio including a wide angle of view is desired for the purpose of being used for an optical system of such an image pickup apparatus. Since, in such an image pickup apparatus, a variety of optical members, including a low-pass filter, a color correction filter, etc., are disposed between the rearmost portion of the zoom lens and the image sensor, a lens system having a relatively long back focal distance is required for the optical system. In addition, in the case of a color camera using an image sensor for color images, a zoom lens excellent in telecentricity on the image side is desired for an optical system of the color camera so as to prevent color shading.
Heretofore, there have been proposed a variety of wide-angle two-unit zoom lenses of the so-called short zoom type each of which is composed of a first lens unit of negative refractive power and a second lens unit of positive refractive power, the separation between the first lens unit and the second lens unit being varied to effect the variation of magnification. In such an optical system of the short zoom type, the variation of magnification is effected by moving the second lens unit of positive refractive power, and the compensation for the shift of an image point due to the variation of magnification is effected by moving the first lens unit of negative refractive power.
In such a lens construction composed of two lens units, the zoom magnification thereof is 2xc3x97 or thereabout. Further, in order to make the entirety of a lens system in a compact form while having a high variable magnification ratio greater than 2xc3x97, there have been proposed, for example, in Japanese Patent Publication No. Hei 7-3507 (corresponding to U.S. Pat. No. 4,810,072), Japanese Patent Publication No. Hei 6-40170 (corresponding to U.S. Pat. No. 4,647,160), etc., the so-called three-unit zoom lenses in each of which a third lens unit of negative or positive refractive power is disposed on the image side of the two-unit zoom lens so as to correct the various aberrations occurring due to the high variable magnification.
Further, in U.S. Pat. Nos. 4,828,372 and 5,262,897, there is disclosed a three-unit zoom lens in which the second lens unit is composed of six lens elements, as a whole, including two cemented lenses, thereby attaining the high variable magnification of 3xc3x97 or more.
Three-unit zoom lenses satisfying both the back focal distance and the telecentric characteristic have been proposed in, for example, Japanese Laid-Open Patent Application No. Sho 63-135913 (corresponding to U.S. Pat. No. 4,838,666), Japanese Laid-Open Patent Application No. Hei 7-261083, etc. In addition, in Japanese Laid-Open Patent Application No. Hei 3-288113 (corresponding to U.S. Pat. No. 5,270,863), there is disclosed a three-unit zoom lens in which a first lens unit of negative refractive power is fixed and a second lens unit of positive refractive power and a third lens unit of positive refractive power are moved to effect the variation of magnification. However, in these zoom lenses, there are such drawbacks that the number of constituent lens elements of each lens unit is relatively large, the total length of the lens system is great, and the production cost is high.
Further, in recent years, there has been widely used the so-called barrel-retractable zoom lens in which, in order to make the compactness of a camera and the high magnification of a lens system compatible with each other, the separation between the respective adjacent lens units at the time of nonuse of the camera is reduced up to the separation different from that at the time of use of the camera, thereby lessening the amount of protrusion of the zoom lens from the camera body. However, in a case where, as in the conventional zoom lenses, the number of constituent lens elements of each lens unit is large and, as a result, the length of each lens unit on the optical axis is great, or in a case where the amount of movement of each lens unit during zooming and during focusing is large and the total lens length is, therefore, great, it is sometimes impossible to attain the desired length of the zoom lens as retracted.
Further, in the zoom lens disclosed in Japanese Laid-Open Patent Application No. Hei 7-261083, a convex lens (positive lens) is disposed on the most object side of the first lens unit of negative refractive power, so that there is such a drawback that an increase of the outer diameter of the zoom lens when made to have a wide angle is inevitable. In addition, in this zoom lens, since the focusing onto a close object is effected by moving the first lens unit of negative refractive power, there is such a drawback that the construction of a lens mounting mechanism is complicated in combination with the movement for zooming.
Further, in U.S. Pat. No. 4,999,007, there is disclosed a three-unit zoom lens in which each of the first lens unit and the second lens unit is composed of a single lens. However, in this zoom lens, the total lens length at the wide-angle end is relatively great, and, because the distance between the first lens unit and the stop at the wide-angle end is large, the height of incidence of an off-axial ray of light is large to increase the diameter of a lens element of the first lens unit. Therefore, there is such a drawback that the entirety of a lens system becomes large.
In view of the above-mentioned drawbacks of the conventional zoom lenses, an object of the invention is to provide a zoom lens which is suited for a photographic system using a solid-state image sensor, has a high variable magnification ratio despite being compact and small in diameter with less constituent lens elements, and has excellent optical performance, and to provide an optical apparatus having the zoom lens.
To attain the above object, in accordance with an aspect of the invention, there is provided a zoom lens, which comprises, in order from an object side to an image side, a first lens unit of negative optical power, the first lens unit including a negative meniscus lens having a concave surface facing the image side and a positive meniscus lens having a convex surface facing the object side, a second lens unit of positive optical power, the second lens unit including a cemented lens of positive optical power as a whole disposed on the most image side of the second lens unit, and a lens having a concave surface facing the image side and adjoining a surface on the object side of the cemented lens, and a third lens unit of positive optical power, wherein a separation between the first lens unit and the second lens unit and a separation between the second lens unit and the third lens unit are varied to effect variation of magnification.
In accordance with another aspect of the invention, there is provided a zoom lens, which comprises, in order from an object side to an image side, a first lens unit of negative optical power, the first lens unit including a negative meniscus lens having a concave surface facing the image side and a positive meniscus lens having a convex surface facing the object side, a second lens unit of positive optical power, the second lens unit including a negative lens of bi-concave form, a positive lens disposed on the object side of the negative lens of bi-concave form and having a convex surface facing the object side, and a cemented lens of positive optical power as a whole disposed on the image side of the negative lens of bi-concave form, and a third lens unit of positive optical power, wherein a separation between the first lens unit and the second lens unit and a separation between the second lens unit and the third lens unit are varied to effect variation of magnification.
In accordance with a further aspect of the invention, there is provided a zoom lens, which comprises, in order from an object side to an image side, a first lens unit of negative optical power, the first lens unit including a negative meniscus lens having a concave surface facing the image side and a positive meniscus lens having a convex surface facing the object side, a second lens unit of positive optical power, the second lens unit including, in order from the object side to the image side, one or two positive lenses, a negative lens of bi-concave form, and a cemented lens of positive optical power as a whole, and a third lens unit of positive optical power, wherein a separation between the first lens unit and the second lens unit and a separation between the second lens unit and the third lens unit are varied to effect variation of magnification, and wherein the zoom lens satisfies the following conditions:
0.5 less than fc/f2 less than 2.0
0.5 less than (Ra+Rb)/(Raxe2x88x92Rb) less than 2.5
0.3 less than |fn|/f2 less than 2.0
0.5 less than (rd+Rc)/(Rdxe2x88x92Rc) less than 2.5
where fc is a focal length of the cemented lens in the second lens unit, fn is a focal length of the negative lens in the second lens unit, f2 is a focal length of the second lens unit, Ra is a radius of curvature of a surface on the object side of the cemented lens in the second lens unit, Rb is a radius of curvature of a surface on the image side of the negative lens in the second lens unit, and Rc and Rd are radii of curvature of lens surfaces on the object side and the image side, respectively, of the positive lens disposed on the most object side of the second lens unit.
In accordance with a still further aspect of the invention, there is provided a zoom lens, which comprises, in order from an object side to an image side, a first lens unit of negative optical power, the first lens unit including a negative lens and a positive lens, a second lens unit of positive optical power, the second lens unit consisting of a cemented lens and one positive lens, and a third lens unit of positive optical power, the third lens unit including a positive lens, wherein a separation between the first lens unit and the second lens unit and a separation between the second lens unit and the third lens unit are varied to effect variation of magnification.
In accordance with a still further aspect of the invention, there is provided a zoom lens, which comprises, in order from an object side to an image side, a first lens unit of negative optical power, a second lens unit of positive optical power, and a third lens unit of positive optical power, the third lens unit consisting of one or two lenses including a positive lens, wherein a separation between the first lens unit and the second lens unit and a separation between the second lens unit and the third lens unit are varied to effect variation of magnification, and wherein the zoom lens satisfies the following conditions:
ndp3 less than 1.5
vdp3 greater than 70.0
where ndp3 and vdp3 are a refractive index and Abbe number, respectively, of material of the positive lens in the third lens unit.
In accordance with a still further aspect of the invention, there is provided a zoom lens, which comprises, in order from an object side to an image side, a first lens unit of negative optical power, a second lens unit of positive optical power, and a third lens unit of positive optical power, wherein a separation between the first lens unit and the second lens unit and a separation between the second lens unit and the third lens unit are varied to effect variation of magnification, and wherein, during the variation of magnification from a wide-angle end to a telephoto end with an infinitely distant object focused on, the third lens unit moves monotonically toward the image side or moves with a locus convex toward the image side, and the zoom lens satisfies the following condition:
0.08 less than M3/fw less than 0.4
where M3 is an amount of movement of the third lens unit toward the image side during the variation of magnification from the wide-angle end to the telephoto end with an infinitely distant object focused on, and fw is a focal length of the zoom lens at the wide-angle end.
In accordance with a still further aspect of the invention, there is provided a zoom lens, which comprises, in order from an object side to an image side, a first lens unit of negative optical power, the first lens unit consisting of, in order from the object side to the image side, a negative lens and a positive lens, a second lens unit of positive optical power, and a third lens unit of positive optical power, wherein a separation between the first lens unit and the second lens unit and a separation between the second lens unit and the third lens unit are varied to effect variation of magnification, wherein, with an infinitely distant object focused on, the third lens unit is located nearer to the image side at a telephoto end than at a wide-angle end, and wherein the zoom lens satisfies the following condition:
0.7 less than |f1/ft| less than 1.0
where f1 is a focal length of the first lens unit, and ft is a focal length of the zoom lens at the telephoto end.
In accordance with a still further aspect of the invention, there is provided a zoom lens, which comprises, in order from an object side to an image side, a first lens unit of negative optical power, the first lens unit consisting of, in order from the object side to the image side, a negative lens and a positive lens, a second lens unit of positive optical power, and a third lens unit of positive optical power, focusing being effected by moving the third lens unit, wherein a separation between the first lens unit and the second lens unit and a separation between the second lens unit and the third lens unit are varied to effect variation of magnification, and wherein, during the variation of magnification from a wide-angle end to a telephoto end with an infinitely distant object focused on, the third lens unit moves monotonically toward the image side or moves with a locus convex toward the image side, and the zoom lens satisfies the following conditions:
0.08M3/fw less than 0.4
0.7 less than |f1/ft| less than 1.0
1.45 less than f3/ft less than 2.0
0.63 less than f2/ft less than 0.8
where M3 is an amount of movement of the third lens unit toward the image side during the variation of magnification from the wide-angle end to the telephoto end with an infinitely distant object focused on, fw and ft are focal lengths of the zoom lens at the wide-angle end and the telephoto end, respectively, and f1, f2 and f3 are focal lengths of the first lens unit, the second lens unit and the third lens unit, respectively.
Further, an optical apparatus according to the invention comprises a zoom lens set forth in accordance with any one of the above aspects of the invention.
The above and further objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.